This invention relates to a floating-caliper spot-type disc brake with a rotating brake disc, a non-rotating brake support member which is secured in position on one side of the brake disc, partly extends across the periphery of the brake disc, guides a brake caliper axially slidably between guiding surfaces parallel to the brake-disc axis and supports the caliper in the circumferential direction of the brake disc. The brake caliper is connected to brake shoes disposed on opposite sides of the brake disc via its legs extending parallel to the brake disc, a first brake shoe of which is guided and supported in the brake support member on the fastening side of the brake support member.
A floating-caliper spot-type disc brake of the aforementioned type is known from German Pat. DE-OS No. 2,408,519. The brake support member projects above the brake disc with two arms which extend parallel to the brake-disc axis and have confronting projections on both sides of the brake disc whose ends form the guiding surfaces. The projections engage into guiding grooves of the brake caliper whose bottom surfaces extend parallel to the brake-disc axis. The clearance between the guiding surfaces and the groove bottoms being low, ease of axial slidability of the brake caliper is ensured.
The brake shoe located on the fastening side of the brake support member is movable into engagement with the brake disc by an actuating piston arranged in the leg of the brake caliper, while the brake shoe associated with the other leg is in positive engagement with the brake-caliper leg and is moved into engagement with the brake disc through the reaction force of the actuating piston. When rotation of the brake disc is slowed down, first the brake shoe close to the piston and supported in the brake support member will move into engagement with the brake disc, thereby transmitting all frictional forces occurring to the brake support member direct. Only then will the brake shoe secured in position in the brake-caliper leg move into engagement with the brake disc and the frictional forces tend to displace the brake caliper in the main direction of rotation of the brake disc in order to support the caliper at the brake support member's guiding surfaces provided. However, since on the side close to the brake support member the brake caliper is in frictional engagement with the brake support member through the piston frictionally engaged with the brake shoe supported in the brake support member, overcoming of the clearances between brake caliper and brake support member caused by the guidings will cause the brake caliper to assume an inclined position resulting in wedge-shaped wear of the brake shoes. When the disc brake is released, the brake caliper will no longer return to its initial position, and on another braking operation its angle of inclination will become still greater until the brake caliper is supported by abutment on the guiding surfaces on the disc exit and disc entry sides, resulting in maximum wedge-shaped wear. At this stage, any further increase in the angle of inclination is only possible by deflection of the arm projecting above the brake disc and serving as a support for the brake caliper.